Years of the Trees 1090
The Valar make war on Melkor for the sake of the Elves. Over the next two years Melkor is defeated, and then forced to retreat into Utumno.
J.R.R. Tolkien, Christopher Tolkien (ed.), Morgoth's Ring, "Part Two. The Annals of Aman: Second section of the Annals of Aman", pp. 74-75